紫色土坡耕地可溶性有机碳淋失特征

Characteristics of Dissolved Organic Carbon Leaching from Sloping Cropland in the Purple Soil

可溶性有机碳(dissolved organic carbon,DOC)在土壤-水界面的径流迁移是土壤有机碳损失的主要形式之一,其迁移损失对土壤有机碳库的源汇功能有重要的影响。为探明紫色土坡耕地DOC的径流迁移特征,利用可测壤中流的径流小区观测壤中流DOC的迁移,结合夏玉米不同生长期土壤DOC含量动态变化分析,研究紫色土壤中流DOC淋失过程与通量。结果表明,土壤DOC含量在玉米生长期逐渐增加,到抽雄期达到最大值,收获期逐渐降至最低。2009—2011年壤中流平均径流量为264 mm,占夏季径流量的68%,表明壤中流是紫色土坡耕地径流的主要形式。壤中流径流量与降雨量呈现极显著正相关性(P<0.01),与降水强度相关性不显著。壤中流过程DOC质量浓度表现为先升后降再趋于稳定的趋势,且与径流速率呈极显著正相关关系(P<0.01)。3年内次降雨产流事件中壤中流DOC质量浓度为1.7～4.6 mg·L^(-1),平均为3.2 mg·L^(-1)。壤中流DOC迁移负荷分别为565.5、802.1和1 090.1mg·m^(-2),平均年累积迁移负荷为819.2mg·m^(-2)。DOC淋失量在玉米不同生长时期变化较为明显,主要发生在抽雄期至成熟期,淋失总量为658.4mg·m^(-2),占年平均淋失负荷的81%,与玉米生长期土壤DOC含量变化趋势基本一致。研究结果可为调控紫色土坡耕地DOC迁移淋失及评价土壤有机碳平衡提供一定的参考和依据。

Runoff is a major driver for dissolved organic carbon(DOC)diffusing into aquatic ecosystems.The transportation of DOC during storm events could have measurable impacts on the global carbon cycle.This study aimed to gain insight into the process and flux of transport of DOC in runoff as affected by rainfall characteristics.A free-drain lysimeter experiment was conducted to quantify dissolved organic carbon leaching losses(2009^-2011)in sloping cropland in the purple soil area,southwestern China.Soil DOC concentrations increased distinctly from sowing to stamen stage,and then decreased to the minimum at harvest in the maize grown season.The average annual discharge of the interflows was 264 mm,accounting for 68%of total runoff in the rainy season in 2009^-2011.It indicated that interflow was the main transport pathway of dissolved organic carbon in the rainy season.There was a significant positive correlation between the discharges of the interflow and rainfall.DOC concentrations increased at the initial period of a rainfall event and declined steadily,and it had a positive correlation with interflow discharge velocity.The average DOC concentrations in interflow were ranged from 1.7 to 4.6 mg·L^-1,with an average of 3.2 mg·L^-1.Annual loss fluxes of DOC through interflow were 565.5,802.1 and 1 090.1 mg·m^-2,respectively,during the experiment period,with an average of 819.2 mg·m^-2.DOC leaching flux through the interflow showed clear seasonal patterns,and largely occurred in the stages from stamen to maturity of maize with a flux of 658.4 mg·m^-2,about 81%of the annual total loss flux.This result responded with seasonal change of soil DOC concentrations during corn growth.The interflow discharge monitoring method used in this study proved to be useful and effective for quantifying DOC leaching losses at the field scale in hillslope cropland areas.This research will provide some basis data in regulating DOC leaching of purple soil sloping farmlands and evaluating the balance of soil organic carbon.